DOCSLIB.ORG

Synthesis of Nanocrystalline Boron Carbide by Direct Microwave Carbothermal Reduction of Boric Acid

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Synthesis of Nanocrystalline Boron Carbide by Direct Microwave Carbothermal Reduction of Boric Acid Hindawi Journal of Nanomaterials Volume 2017, Article ID 3983468, 8 pages https://doi.org/10.1155/2017/3983468 Research Article Synthesis of Nanocrystalline Boron Carbide by Direct Microwave Carbothermal Reduction of Boric Acid Rodolfo F. K. Gunnewiek, Pollyane M. Souto, and Ruth H. G. A. Kiminami Department of Materials Engineering, Federal University of Sao˜ Carlos, Rod. Washington Luiz, km 235, 13565-905 Sao˜ Carlos, SP, Brazil Correspondence should be addressed to Rodolfo F. K. Gunnewiek; [email protected] Received 24 January 2017; Accepted 12 March 2017; Published 27 March 2017 Academic Editor: Stefano Bellucci Copyright © 2017 Rodolfo F. K. Gunnewiek et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The excellent physical and chemical properties of boron carbide make it suitable for many applications. However, its synthesis requires a large amount of energy and is time-consuming. Microwave carbothermal reduction is a fast technique for producing well crystallized equiaxial boron carbide nanoparticles of about 50 nm and very few amounts of elongated nanoparticles were also synthesized. They presented an average length of 82 nm and a high aspect ratio (5.5). The total reaction time was only 20 minutes, which disfavor the growing process, leading to the synthesis of nanoparticles. Microwave-assisted synthesis leaded to producing boron-rich boron carbide. Increasing the forward power increases the boron content and enhances the efficiency of the reaction, resulting in better crystallized boron carbide. 1. Introduction (with 20%-at. of carbon) and even high carbon content boron carbide B11.4C3.6 (B3.17C), which corresponds to 24%-at. of Boron carbide is covalent carbide, which presents some of the carbon [2, 14–16]. The composition of boron carbide affects best physical and chemical properties. B4C is the third hardest its properties, since carbon-rich crystals approach the ideal materialandshowshighYoung’smodulus,highmeltingpoint ∘ crystal and have the lowest electrical conductivity, while (2450 C without decomposing), excellent chemical resis- 3 boron-rich crystals are more resistant to radiation damage. tance, very low density (2.52 g/cm ), low stiffness, excellent However, the ideal boron carbide structure, B4C, is composed thermoelectric properties, and good cross section absorption of B11C icosahedra and C-B-C chains comprising the longest of thermal neutrons. These properties make it suitable for diagonal in the rhombohedral structure [2]. numerous applications from wear resistant components and Boron carbide can be synthesized by different methods, cutting tools to high temperature thermocouples and neu- for example, magnesiothermic and aluminothermic reduc- tron absorbers [1–5]. Boron carbide can also be used as a tion, both of which are exothermic reductions of B2O3 in the precursor or reduction agent to produce boron nitride and presence of metallic magnesium or aluminum, and a carbon transition-metal diborides (TiB2,ZrB2,HfB2,andCrB2)[6– source [2, 16–18], vapor phase reaction [2], polymer precur- 10] and recently has been applied in gamma ray scintillator sors [17, 19–22], liquid phase reaction [23], and solid state and neutron detectors and as high efficiency thermoelectric reaction [15] are other alternative routes to producing boron material [11, 12]. carbide. The carbothermal reduction, a technique widely It belongs to the rhombohedral lattice R3m space group, used in industry and laboratory to produce mostly carbides, although a recent paper describes a second B4Cphasewith including boron carbide, consists of reacting an oxide (boron monoclinic structure, reopening the discussion about the oxide) and a carbon source at high temperatures, which boron carbide structure [13]. Boron carbide can be found normally takes several hours to complete [2]. in a wide range of carbon and boron compositions: from An inexpensive and efficient way to synthesize boron B11.4C (with 8%-at. of carbon) to the most well-known B4C carbide by the aforementioned technique is using boric acid 2 Journal of Nanomaterials Multimodal applicator power Forward Ceramic tube Stirrer Argon inlet Alumina boat and precursors ermal insulator Figure 1: Schematic diagram of the microwave reaction system. and carbon black or charcoal as starting materials [24–28]. reduction of boric acid. Microwave forward power, which The general reaction between boric acid and carbon is very influences the synthesis of boron carbide, is also evaluated for simple: first the boric acid dehydrates and is converted to both stoichiometric and hyperstoichiometric raw materials. boron anhydride, followed by the reduction to elemental boron by carbon, and finally the reaction of this species 2. Experimental Procedures with carbon, yielding boron carbide. This reaction is efficient 2 and pure boron carbide can be produced at temperatures Disordered carbon black with high surface area (263.2 m /g) ∘ above 1400 C and normally a long reaction time (1 h to 5 h) and pure boric acid (Merck, >99%) were used in this [2]. The reaction time and temperature, heating rate, and experiment. The raw materials, at a ratio of 4 : 7 mol of boric boron/carbon rate are essential parameters to control the acid/carbon (R4B), were suspended in ethanol (the boric acid dissolved completely) and stirred continuously on a hot plate final average particles size. Increasing both the reaction time ∘ and temperature enhances B4Csynthesis[25].Higherheating at 50 C for one hour to partially evaporate the solvent, which rates cause the raw materials to reach the final temperature rendered the suspension pasty. The partially dried paste was extruded into pellets and completely dried in a kiln at around rapidly, practically without undergoing an intermediate tem- ∘ perature. Higher temperature favors reactions in the vapor 50 C (this procedure was necessary to prevent the removal state and high levels of nucleation, which can result in finer oftheprecursorsbytheargonfluxduringthereaction).In particles. addition, to determine whether it is possible to synthesize Finer nanoparticles are hard to synthesize, because, high boron-content boron carbide, another precursor was besides the high nucleation rate caused by high temperature, prepared with a boric acid to carbon ratio of 8 : 7 (R8B). About the particles growing is also observed due the long reaction 2gofthepelletswasspreadonasmallalumina/mulliteboat time. This factor can be avoided by the use of microwaves, (50mminlength)andplacedinamicrowaveoven(2.45GHz, which reduces considerably the time and prevents excessive Cober, USA), whose reaction chamber was cleaned for 10 min particle growth. Hard materials such as TiC, TaC, WC, with an argon flow set at 1.0 L/min. The reaction systems were nanometric titanium carbide, and carbonitride have been designed to protect the oven and control the atmosphere, as produced by microwave irradiation [29–33]. depicted in Figure 1. The reaction system consisted in a low Nitrides and carbides are very difficult to sintering due porosity ceramic tube coated with refractory fiber (to avoid to their reduced diffusion coefficients. The use of nanos- heat loss) placed inside the oven cavity. An argon inlet was tructured boron carbide can enhance the sintering, because connected to the tube at one end and a gas collector at the the diffusion is accelerated due to the high surface energy, other. The rectangular boat crucible containing the precursor also leading to obtaining ceramics with controlled and finer wasinsertedintothetubeatthecenteroftheovencavity. microstructure (the benefits of finer microstructure in the The microwave forward power was set at 1.8 and 2.1 kW properties (e.g., mechanical, electrical, and others) are well for each composition. The samples were allowed to cool in known). The sintering step is influenced by the initial boron an argon atmosphere to prevent reoxidation, which took no carbide particle size and shape and also by additives, such more than 40 min. The cooled powders were deagglomerated as free carbon, which prevents the formation of boron oxide and ground in a mortar and sifted through a 325-mesh sieve. thin film [34] and a low melting point at the grain boundary, To determine the phase constitution, X-ray diffraction (XRD) aiding mass diffusion and also controlling grain growth [17]. patterns of the powders were recorded in a Siemens D5005 This paper describes a fast and efficient approach for diffractometer using copper K radiation ( =1,5406A).˚ preparing nanocrystalline B4C by microwave carbothermal Crystallite size was calculated using Scherrer’s relation Journal of Nanomaterials 3 350 (proportion of 4 : 7 of H3BO3/C), the formation of boron carbide is evident, and the well-defined peaks in the XRD 300 pattern are very clear. The peaks correspond to rhombohedral B4C for R4B-1 and R4B-2 and are consistent with JCPDS card 250 number 35-798, although smaller peaks corresponding to unreacted orthoboric acid, H3BO3, and a band of disordered 200 carbon were detected. Moreover, the intensity of the peaks increased along with the power level, possibly indicating 150 more crystalline boron carbide and/or more effective reac- Intensity (a.u.) Intensity tion, yielding a larger total amount of boron carbide when 100 synthesized at higher power. When the boric acid content in the precursor was doubled, the reaction
Load more

Recommended publications
  • Superhard and Superconducting B6C
    Superhard and Superconducting B6C Kang Xia a, Mengdong Ma b, Cong Liu a, Hao Gao a, Qun Chen a, Julong He b, Jian Sun a,*, Hui-Tian Wang a, Yongjun Tian b, and Dingyu Xing a a National Laboratory of Solid State Microstructures, School of Physics and Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China b State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China ABSTRACT Crystal structure searching and ab initio calculations have been used here to explore low-energy structures of boron carbides under high pressure. Under pressures of 85–110 GPa, a metastable B6C with R3 m symmetry is found to be energetically more stable than the mixture of previous B4C and elemental boron. This B6C is a rhombohedral structure and contains mooncake-like B24 clusters with stuffing of C2 pairs. The mechanical and dynamical stabilities of this structure at ambient pressure are confirmed by its elastic constants and phonon dispersions. The bulk modulus and shear modulus of this newly predicted B6C at ambient pressure reach high values of 291 GPa and 272 GPa, respectively. The Vickers hardness is calculated to be around 48 GPa, and its melting temperature at ambient pressure is estimated to be around 2500 K, indicating that this metastable B6C is a potential superhard material with very good thermal stability. Interestingly, this superhard B6C structure is also found to be superconducting and its superconducting critical temperature (Tc) is evaluated to be around 12.5 K at ambient pressure by electron-phonon coupling. * Corresponding author. E-mail address: [email protected] 1.
    [Show full text]
  • Volumetric Determination of Boron in Boron Carbide V
    B. A. R. C.-1017 ei GOVERNMENT OF INDIA ATOMIC ENERGY COMMISSION VOLUMETRIC DETERMINATION OF BORON IN BORON CARBIDE V. K. Manchanda and M. S. Subramanian Radiochemistry Division BHABHA ATOMIC RESEARCH CENTRE BOMBAY, INDIA 1979 B. A. R.C.-1017 GOVERNMENT OF INDIA ATOMIC ENERGY COMMISSION U erf < ffl VOLUMETRIC DETERMINATION OF BORON IN BORON CARBIDE by V.K. Manchanda and M. S. Subramantan Radlochernlstry Division BHABHA ATOMIC RESEARCH CENTRE BOMBAY, INDIA 1979 INIS Subject Category : Bll Descriptor a : BORON CARBIDES BORON QUANTITATIVE CHEMICAL ANALYSIS TITRATION ACCURACY ABSTRACT Boron carbide is used for oontrol rods and as a shielding material In nuclear reactors. As such, the boron carbide must conform to rigid chemical specifications. Impurities present have a significant effect on the life time of the control rods under conditions of high temperature and i neutron flux. Therefore, methods for the accurate determination of the various constituents in boron carbide is of utmost importance. This-report discusses p\volumetric procedure for i •_ . •' i : ((.•>;•" ••%. the, determination of boron content In boron carbide/ '•••>',••. A VOLtCIKTRIC DET3SIINATI0N 0? BCRON IN BORON CAR3IDE by V.K. Jfenchanda and M.S. Subramanian IU7R0DVCT10N Boron carbide is an important nuclear material a.3 it is used in nuclear reactors for control rods and as a shielding material « Preparation of boron carbide yields a product often contaminated with either unreacted carbon or boric acid. These impurities affect the physical, chemical and neutron absorption properties of the material, Particularly under conditions of high temperature and neutron flux in a reactor, tlie life time of the control rods depends on its composition.
    [Show full text]
  • The Formation and Reactivity of I BORON CARBIDE and Related
    University of Plymouth PEARL https://pearl.plymouth.ac.uk 04 University of Plymouth Research Theses 01 Research Theses Main Collection 1970 The Formation and Reactivity of BORON CARBIDE and related materials JONES, JAMES ALFRED http://hdl.handle.net/10026.1/1880 University of Plymouth All content in PEARL is protected by copyright law. Author manuscripts are made available in accordance with publisher policies. Please cite only the published version using the details provided on the item record or document. In the absence of an open licence (e.g. Creative Commons), permissions for further reuse of content should be sought from the publisher or author. The Formation and Reactivity of I BORON CARBIDE and related materials A Thesis presented for the Research Degree of DOCTOR OF PHILOSOPHY of the COUNCIL FOR NATIONAL ACADEMIC AWARDS London by JAMES ALFRED JONES Department of Chemistry Plymouth Polytechnic Plymouth, Devon- February^ 1970o F'.V flCCH. i'iC. 1 CLASS, T Shi LJl JoH 13' ABSTRACT 1 The formation of boron carbide, (CBC)*B^^0*^(3^0 is re• viewed with special reference to newer production methods and fabrication techniques. Its crystal structure and the nature of its bonding are discussed in relation to those of other borides and carbides. Information so far available on the sintering of this material is summarised in relation to its reactivity. Sintering into monolithic compoaentBcan only be achieved by hot pressing at pressures between 200 and 300 Kgcm'^ and at temperatures above 2000°C preferably at about 2,300^0 for the most rapid achievement of theoretical density, i.e.
    [Show full text]
  • The 5-Th Element a New High Pressure High Temperature Allotrope
    The 5-th element A new high pressure high temperature allotrope Von der Fakultät für Chemie und Geowissenschaften Der Universität Bayreuth zur Erlangung der Würde eines Doctors der Naturwissenschaften -Dr. rer. nat.- Dissertation vorgelegt von Evgeniya Zarechnaya aus Moskau (Russland) Bayreuth, April 2010 TABLE OF CONTENTS SUMMARY................................................................................................................................................... 1 ZUSAMMENFASSUNG.............................................................................................................................. 3 1 INTRODUCTION....................................................................................................................... 6 1.1 History of the discovery of boron................................................................................................... 6 1.2 Basic chemistry and crystal-chemistry of boron........................................................................... 7 1.3 Boron in natural systems ................................................................................................................ 9 1.4 Physical properties of boron and its application ........................................................................ 12 1.5 Boron at high pressure.................................................................................................................. 15 1.6 Experimental techniques and sample characterization ............................................................
    [Show full text]
  • Processing of Reaction-Bonded B4C–Sic Composites in a Single-Mode Microwave Cavity
    Available online at www.sciencedirect.com CERAMICS INTERNATIONAL Ceramics International 39 (2013) 1215–1219 www.elsevier.com/locate/ceramint Processing of reaction-bonded B4C–SiC composites in a single-mode microwave cavity Anthony Thuaulta,n, Sylvain Marinela,b, Etienne Savarya,c, Romain Heugueta, Se´bastien Saunierc, Dominique Goeuriotc, Dinesh Agrawalb aCRISMAT Laboratory UMR 6508 CNRS-ENSICAEN-UCBN, 6 Boulevard du Mare´chal Juin, 14050 Caen Cedex, France bMaterials Research Institute, Materials Research Laboratory Building, The Pennsylvania State University, University Park, PA 16802, USA cDe´partement Me´canique et Proce´de´s d’e´laboration, Centre des Sciences des Mate´riaux et des Structures, Ecole Nationale Supe´rieure des Mines de Saint- Etienne, 42023 Saint-Etienne Cedex 2, France Received 5 July 2012; received in revised form 16 July 2012; accepted 16 July 2012 Available online 24 July 2012 Abstract In this study, the reaction sintering of boron carbide, which consists in doing reactive infiltration of molten silicon throughout a porous sample made of B4C and carbon graphite was investigated. Thus, it has been shown that a single-mode microwave cavity can be successfully used to produce reaction-bonded B4C–SiC composite. A specific package, consisting of a SiC based susceptor and a boron nitride based insulating container, was used to heat up the B4C–Si system using a single-mode microwaves cavity under an Ar–H2 atmosphere. Pore-free B4C–SiC composite successfully produced consists of a mixture of B4C and polygonal shaped b-SiC within a residual silicon matrix. The indentation technique permits to determine mechanical properties of the samples which are compared to those obtained conventionally.
    [Show full text]
  • Nitrogen Containing Carbon Nanofibers As Non-Noble Metal Cathode Catalysts In
    Nitrogen Containing Carbon Nanofibers as Non-Noble Metal Cathode Catalysts in PEM and Direct Methanol Fuel Cells Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Elizabeth Joyce Biddinger, B.S.ChE Graduate Program in Chemical Engineering * * * * The Ohio State University 2010 Dissertation Committee: Professor Umit S. Ozkan, Advisor Professor Jeffrey Chalmers Professor Stuart Cooper Copyright by Elizabeth Joyce Biddinger 2010 ABSTRACT PEM and direct methanol fuel cells (DMFC) have great potential for use as alternative fuel energy conversion devices. Before this potential can be realized, however, performance improvements must be made and material costs need to be reduced. The limiting reaction in the PEMFCs and DMFCs is the oxygen reduction reaction (ORR), which occurs at the cathode. In an attempt to improve the reaction kinetics, substantial loadings of Pt catalysts are required on the cathode. This significantly increases the overall cost of the fuel cell. Also, in DMFCs, methanol crossover from the anode allows for competing reactions at the cathode catalyst to occur, reducing the power output of the fuel cell further. As the demand for fuel cells increase, the demand for Pt will far outpace the supply of Pt. Replacements studied for Pt cathode catalysts include Pt alloys, other noble metals, chalcogenides and nitrogen-containing carbons. Nitrogen-containing carbons made from simple precursors can provide an economical replacement to Pt catalysts. Before this can be realized, improvements in the activity and selectivity of the nitrogen- containing carbons need to occur. ii The work presented here involves the study of nitrogen-containing carbon nanostructures (CNx) as ORR catalysts for PEMFCs and DMFCs.
    [Show full text]
  • Material Development for India's Nuclear Power Programme
    Sadhan¯ a¯ Vol. 38, Part 5, October 2013, pp. 859–895. c Indian Academy of Sciences Material development for India’s nuclear power programme AKSURI Materials Group, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India e-mail: [email protected] Abstract. The area of materials research has registered a phenomenal growth in the recent years, assiduously accepting and assimilating ideas, concepts and analyti- cal as well as experimental methodologies and techniques form almost all scientific disciplines, thereby demonstrating its remarkably multidisciplinary and interdiscipli- nary character. The focus of the materials programme of this centre is to provide materials, processes and processing solutions to the emerging needs of evolving indigenous nuclear energy systems by proactive research and development on a con- tinuing basis. The initial stage of our activities was formulated around three stage Indian nuclear power programme. In stage I, material issues related to in-core mate- rials with emphasis on development of fabrication routes of zirconium alloys for structural application were addressed. Subsequently the thrust areas were develop- ment and characterization of mixed oxide fuel, advanced zirconium alloys, structural steels, superalloys, neutron absorber materials based on boron carbides and borides, and shape memory alloys. The research was useful for in-service performance evalu- ation, safety assessment, residual life estimation and life extension of nuclear reactors built during stage I i.e., PHWRs and BWRs. It also included developments which would permit rapid expansion of nuclear power initially through fast breeder reactor based on mixed oxide fuel and later based on metallic fuels. For the 3rd stage, multi- layer coatings, graphite coolant tube, BeO, refractory metals and alloys, heat-treated zirconium alloys are being developed for CHTR, ADSS and AHWR.
    [Show full text]
  • Structural Stability and Mechanism of Compression
    Structural stability and mechanism of compression of stoichiometric B13C2 up to 68GPa Irina Chuvashova, Elena Bykova, Maxim Bykov, Volodymyr Svitlyk, Leonid Dubrovinsky, Natalia Dubrovinskaia To cite this version: Irina Chuvashova, Elena Bykova, Maxim Bykov, Volodymyr Svitlyk, Leonid Dubrovinsky, et al.. Structural stability and mechanism of compression of stoichiometric B13C2 up to 68GPa. Scientific Reports, Nature Publishing Group, 2017, 7, 9 p. 10.1038/s41598-017-09012-8. hal-01691833 HAL Id: hal-01691833 https://hal.archives-ouvertes.fr/hal-01691833 Submitted on 24 Jan 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. www.nature.com/scientificreports OPEN Structural stability and mechanism of compression of stoichiometric B13C2 up to 68GPa Received: 15 March 2017 Irina Chuvashova1,2, Elena Bykova 2,3, Maxim Bykov2, Volodymyr Svitlyk 4, Accepted: 14 July 2017 Leonid Dubrovinsky2 & Natalia Dubrovinskaia1 Published: xx xx xxxx Boron carbide is a ceramic material with unique properties widely used in numerous, including armor, applications. Its mechanical properties, mechanism of compression, and limits of stability are of both scientifc and practical value. Here, we report the behavior of the stoichiometric boron carbide B13C2 studied on single crystals up to 68 GPa.
    [Show full text]
  • METALS Aid CERAMICS DIVISION
    -s-- r . Z Ls> > ORNL-4870 METALS aid CERAMICS DIVISION Annual Progress Report Period Ending June 30, 1973 "1 BLANK PAGE t Printed in the Untied States c* Amtfitt. Available from Nation*) Technical information Service U.S. Department of Commerce 5285 Port Royal Road. Springfield, Virginia 22151 Price: °rtnwd Copy $5.45; Micro!*!* S0.9S • ~ • Thit report was prepared as an account of work sponsored by the United Statas Government. Neither the United Statas nor the United States Atomic Energy Commission, nor any of tfc*ir employees, nor any of their contractors, subcontractors, or their employees, rnakat afty warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that m use would not infringe privately owned rights. ORNL-4870 UC 25 - Materials Contract No. W-74C5-«ng-26 METALS ANO CER'«MICS DIVISION ANNUAL PROGRESS REPORT for Period Endtnf June 30.1973 j. H Frye, Jr., Director* J. E. Cunninohem. Associate Director G. M. Adamson. Jr. C. J. McHar«uc P Patriarca i. R. Weir. Jr.* Compiled and Edited by Sigfred Petef too 'Rtwid June 30.1973. preawtt Uwwerutv o* fN©w Owieon Director. -NOTlCI OCTOBER 1973 OAK RlOGE NATIONAL LABORATORY O* R«ie*. Ttmnw 37830 optr»t«dbv UNION CARBIDE CORPORATION for th« U S ATOMIC ENERGY COMMISSI 0\ amim Reports prtviously issued in this series are as follows: ORNL 28 Period Ending March 1, 1948 ORNL 69 Period Ending May 31. 1948 ORNL407 Period Ending July 31. 1949 ORNL 511 Period Ending October 31, 1949 ORNL 583 Period Ending January 31, 1950 ORNL 754 Period Ending April 30.
    [Show full text]
  • LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, E.G. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE {(Roofi
    CPC - C04B - 2021.08 C04B LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE {(roofing granules E04D 7/005)}; CERAMICS (devitrified glass-ceramics C03C 10/00); REFRACTORIES; TREATMENT OF NATURAL STONE Definition statement This place covers: Chemical aspects of the processing of lime, magnesia or dolomite and of molten slag. Compositional aspects of: • inorganic binders, such as hydraulic cements ; • mortars, concrete and artificial stone, e.g. the choice of fillers or active ingredients therefore; • shaped ceramic products, e.g. clay-wares, refractories , non-oxides. Physico-chemical aspects of methods for obtaining mortars, concrete, artificial stones or ceramics , e.g. for delaying the setting time of mortar compositions. Treatment including defibrillating of materials such as fillers , agglomerated or waste materials, or refuse to enhance their filling properties in mortars, concrete or artificial stone. Porous mortars, concrete, artificial stone or ceramic ware, and the preparation thereof. Methods and apparatus for: • burning or slaking lime; • obtaining mineral binders, e.g. Portland cement or hemihydrate plaster; • the expansion of mineral fillers , such as clay, perlite or vermiculite. After- treatment of artificial stones, mortars, concrete and ceramics , e.g. coating or impregnation of green concrete after primary shaping. Non-mechanical treatment of natural stone. Processing powders of inorganic compounds in preparation to the manufacturing of ceramic products . 1 C04B (continued) CPC - C04B - 2021.08 Definition statement The joining of burned ceramics with other articles by heating. References Limiting references This place does not cover: Granulating apparatus B01J 2/00 Mechanical features relating to the working of mortars, concrete, stone, B28 clay-wares or ceramics , e.g.
    [Show full text]
  • 8 Characteristics and Properties of Silicon Carbide and Boron Carbide
    8 Characteristics and Properties of Silicon Carbide and Boron Carbide 1.0 INTRODUCTION In the previous chapter, the structure and composition of the two covalent carbides, i.e., silicon carbide and boron carbide, were reviewed. This chapter is an assessment of the properties and a summary of the fabrication processes and applications of these two compounds. Silicon carbide and boron carbide to a lesser degree are important industrial materials which are produced on a large scale in the form of powders, molded shapes, and thin films. 2.0 CHARACTERISTICS AND PROPERTIES OF SILICON CARBIDE 2.1 Historical Background and Present Status Silicon carbide was first synthesized in 1891 by Acheson by passing an electric current through a mixture of carbon powder and clay. The material was originally thought to be a mixture of carbon and corundum (aluminum oxide) and trademarked Carborundum (CARBOncoRUNDUM). 137 138 Handbook of Refractory Carbides and Nitrides Acheson soon determined that it was actually silicon carbide. The product was an immediate commercial success as an abrasive.t11t21 The Acheson process is still the major production process. In the US, over 115,000 metric tons of silicon carbide were produced in 1994 with a value estimated at $40 million, much of which was for abrasives and metallurgical uses.t31 2.2 Summary of Properties The characteristics and properties of silicon carbide are summarized in Table 8.1 t4j-t10jand reviewed in more detail in Sets. 4-8. Values quoted are for hot-pressed material and are an average of the values reported in the literature. Table 8.1: Summary of Characteristics and Properties of Silicon Carbide.
    [Show full text]
  • Structural Stability and Mechanism of Compression Of
    www.nature.com/scientificreports OPEN Structural stability and mechanism of compression of stoichiometric B13C2 up to 68GPa Received: 15 March 2017 Irina Chuvashova1,2, Elena Bykova 2,3, Maxim Bykov2, Volodymyr Svitlyk 4, Accepted: 14 July 2017 Leonid Dubrovinsky2 & Natalia Dubrovinskaia1 Published: xx xx xxxx Boron carbide is a ceramic material with unique properties widely used in numerous, including armor, applications. Its mechanical properties, mechanism of compression, and limits of stability are of both scientifc and practical value. Here, we report the behavior of the stoichiometric boron carbide B13C2 studied on single crystals up to 68 GPa. As revealed by synchrotron X-ray difraction, B13C2 maintains its crystal structure and does not undergo phase transitions. Accurate measurements of the unit cell and B12 icosahedra volumes as a function of pressure led to conclusion that they reduce similarly upon compression that is typical for covalently bonded solids. A comparison of the compressional behavior of B13C2 with that of α–B, γ–B, and B4C showed that it is determined by the types of bonding involved in the course of compression. Neither ‘molecular-like’ nor ‘inversed molecular-like’ solid behavior upon compression was detected that closes a long-standing scientifc dispute. 1 2 Boron carbide B4C was discovered in 1858, and its crystal structure was frst established in 1934. It belongs to icosahedral boron compounds, a family of crystalline solids with crystal structures based on vari- ous arrangements of B12 icosahedra, which are considered to be some kind of B12 “molecules”. In such solids chemical bonding has been rationalized in terms of polycenter bonds on the B12 closo-cluster (boron icosahe- dron) and two-electron-two-center (2e2c) and two-electron-three-center (2e3c) bonds between the clusters3.
    [Show full text]